Packet transfer delay (PTD) and symmetrical PTD are important for many timing-over-packet techniques. However, currently there appears to be no way to express meaningful service level requirements on packet networks that provide services that rely on the performance of these techniques. Service Level Agreements (SLAs) need predefined and agreed-upon metrics so that customers of telecommunications services can understand the performance characteristics of the services they are buying and to ensure that theses services are compatible with equipment they will connect to the services. Telecommunications service providers also need to know what performance levels they are committing to and equally important, the ability to measure those performance levels in a meaningful way and on a regular basis so that their equipment can take corrective action if the measured performance parameters begin to deteriorate.
One known solution for deriving timing information is based on a concept known as “lucky packet” or fastest packet. The “lucky” packet is the fastest timing packet to transit from a source (e.g. master node) to the destination (e.g. slave node). In the case of adaptive clock techniques associated with circuit emulation services, the fastest packet can be determined using the buffer residence time of each timing packet in the receive buffer of the slave node. Since packets are sent from the master node at regular intervals and retrieved from the slave's receive buffer at regular intervals, the packet with the longest buffer residence time must have transited the network the fastest compared to all other packets in the receive buffer. In the case of timestamp exchange protocols, like Network Time Protocol (NTP) or IEEE1588, the difference between the origination and reception timestamps can be used determine the fastest packet. With reference to prior art FIG. 1, the fastest packet 102, 104, 106, 108 is determined at regular intervals 110, 112, 114, 116. Since each of the fastest packets incurred the least amount of network delay during its respective interval, the variability in determining timing information should be minimal if that information is derived from the fastest packets.
A possible disadvantage of the “lucky packet” technique is that it does not provide a meaningful measure of the overall performance of packet transfer delay. The only packets being measured are ones encountering little or no delay through the network. Another possible disadvantage of this technique is that it requires many consecutive window measurements to determine the stability of the lucky packets. This may require prolonged measurements for each location under test. Management resources may limit the number of tests that can be accomplished in a given period.
Another known technique is to calculate the median packet transfer delay 118, 120, 122, 124 of packets received during each regular interval 110, 112, 114, 116. The median packet transfer delay technique has the same disadvantages as for the ‘lucky packet’ technique.
Another known technique is to measure maximum packet delay variance over regular time intervals, which also may not be sufficient for many real-world situations.
Therefore an improved system or method for measuring network impairments for timing-over-packet networks is desired.